Do cement lines restrict osteoclastic bone resorption?

Bone is constantly remodeled throughout life, but whether the microstructure of the bone affects resorption is unknown. In this present study, longitudinal and transverse devitalized bone slices were cultured in-vitro with rat bone marrow cells to investigate the influence of bone microstructure in directing and regulating bone resorption by osteoclasts. After the 14-day culture period, the average size of resorption areas produced in the longitudinal slices was found to be three times larger than in the transverse slices (p < 0.05). In addition, bone resorption pro-files were consistent with the microstructure of the bone slices. In the longitudinal bone sections resorption areas proceeded more longitudinally than transversely and resorption areas in transverse bone sections were more circular, either contained inside or outside the cement line surrounding the osteon. These results show that the bone microstructure influences osteoclastic resorption and that the cement lines may be the microstructural element that directs and regulates osteoclastic resorption.